As possible applications for RFID devices grow, passive RFID devices, like RFID transponders or tags, are becoming more prevalent and widely used. Most of the largest users of RFID tags are in the supply chain management market place. Here, companies utilize passive RFID tags by the millions to tag consumer products. In a car production process, individual car parts, like doors, stereo, engine components, etc. may be tagged with individual RFID devices in order to keep track of each part of the eventual final product. Other products like clothes are tagged in the supply chain in order to keep an accurate account of every product as it passes from one entity to the next.
Passive RFID tags do not have an internal power source, like a battery. This is done in order to keep costs of the RFID tags low and the size and weight of the tags at a minimum. Because passive RFID tags have no internal power source, they must harvest energy from RF signals produced by external objects. Usually, an RFID reader or interrogator emits an RF field in order to establish a communications link between the RFID reader/interrogator and an RFID device. The RFID devices harvest the inherent energy in the RF field to power their circuitry. Once the RFID device has received power from an external field, it may generate a message and begin transmitting a communication to the RFID reader/interrogator or another receiver. The communications between the interrogator and RFID device are typically initiated to determine some amount of information about the RFID device.
Harvesting RF power is not a new concept. A classic example of RF power harvesting can be seen in old-fashioned crystal radios that draw their power directly from AM radio stations. Some radios harvest enough power to even drive headphones for the radio. A more modern example of RF power harvesting can be found in aftermarket modules that can be connected to a cellular phone and light up when the cell phone rings. The modules harvest the RF signals that are being sent to the cell phone in order to power the lights.
One problem with current identification and security systems is that some companies will buy a single interrogator and the corresponding firmware or chips from a particular vendor and copy the firmware from the purchased devices to use in other interrogators that were not purchased from the original vendor. These companies are exploiting the work of the vendor to produce illicit interrogators that run on the same firmware even though the copies of that firmware were not paid for. Additionally, the vendor would like to ensure that copies of the chips are not being used with other interrogators not purchased from the vendor. In other words, a vendor usually requires a customer to pay for each copy of the chip that is being used in the customer's system. Some entities will buy a particular number of chips but create copies of them for use in more interrogators. These entities are essentially stealing chips from the vendor.
There exists a need for a device that can quickly and easily be used for product and/or brand authentication of a given interrogator without actually taking apart the reader/interrogator or performing an in depth analysis of the reader/interrogator. There also exists a need for a product and method that can be used by a person to quickly query a reader/interrogator in order to determine if it is functioning properly and what if any maintenance is required for that reader/interrogator.
Sometimes in secure access systems, a person will present an RFID device to a reader/interrogator and not receive response. This may be because the holder of the RFID device is not authorized to access the asset that is being protected by the given reader/interrogator. However, it is also possible the reader/interrogator and/or the RFID device may not be functioning properly. There is typically no way for the holder of the RFID device to know the difference between these problems. Furthermore, one problem may require the person to take a certain course of action, like talk to security personnel to show that they are in fact authorized to access the given asset. While another problem may require the person to talk to maintenance personnel to fix the reader/interrogator. It would be much more efficient if the person could learn what the problem was and why they were not granted access to the asset. There do exist some reader/interrogators that will attempt to relay this type of information to a holder of the RFID device by blinking a light, creating a display, or making some noise. However, if the reader/interrogator is not functioning properly, there is no guarantee that this information will be relayed to the holder of the RFID device properly.